Plastic integrated circuit package and method and leadframe for making the package

ABSTRACT

Packages for an integrated circuit die and methods and leadframes for making such packages are disclosed. The package includes a die, a die pad, peripheral metal contacts, bond wires, and an encapsulant. The die pad and contacts are located at a lower surface of the package. The die pad and the contacts have side surfaces which include reentrant portions and asperities to engage the encapsulant. 
     A method of making a package includes providing a metal leadframe having a die pad in a rectangular frame. Tabs extend from the frame toward the die pad. The die pad and tabs have side surfaces with reentrant portions and asperities. A die is attached to the die pad. The die is electrically connected to the tabs. An encapsulant is applied to the upper and side surfaces of the leadframe. Finally, the leadframe is cut in situ so that the die pad and tabs are severed from the frame, the sides of the package are formed, and the package is severed from the leadframe.

RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.10/626,150 entitled PLASTIC INTEGRATED CIRCUIT PACKAGE AND METHOD ANDLEADFRAME FOR MAKING THE PACKAGE filed Jul. 24, 2003, which is acontinuation of U.S. application Ser. No. 10/171,702 entitled PLASTICINTEGRATED CIRCUIT PACKAGE AND METHOD AND LEADFRAME FOR MAKING THEPACKAGE filed Jun. 14, 2002 and issued as U.S. Pat. No. 6,630,728 onOct. 7, 2003, which is a continuation of U.S. application Ser. No.09/615,107 entitled PLASTIC INTEGRATED CIRCUIT PACKAGE AND METHOD ANDLEADFRAME FOR MAKING THE PACKAGE filed Jul. 13, 2000 and issued as U.S.Pat. No. 6,433,277 on Aug. 13, 2002, which is a continuation of U.S.application Ser. No. 09/103,760 entitled PLASTIC INTEGRATED CIRCUITPACKAGE AND METHOD AND LEADFRAME FOR MAKING THE PACKAGE filed Jun. 24,1998 and issued as U.S. Pat. No. 6,143,981 on Nov. 7, 2000.

FIELD OF THE INVENTION

The present invention is to directed toward an improved plastic packagefor an integrated circuit die, and a method of making such a package.

BACKGROUND OF THE INVENTION

Integrated circuit die are conventionally enclosed in plastic packagesthat provide protection from hostile environments and enable electricalinterconnection between the integrated circuit die and printed circuitboards. The elements of such a package include a metal leadframe, anintegrated circuit die, bonding material to attach the integratedcircuit die to the leadframe, bond wires which electrically connect padson the integrated circuit die to individual leads of the leadframe, anda hard plastic encapsulant material which covers the other componentsand forms the exterior of the package.

The leadframe is the central supporting structure of such a package. Aportion of the leadframe is internal to the package, i.e., completelysurrounded by the plastic encapsulant. Portions of the leads of theleadframe extend eternally from the package and are used to connect thepackage externally.

Further background information concerning conventional plasticintegrated circuit packages and leadframes is contained in chapter 8 ofthe book Microelectronics Packaging Handbook (1989), which was edited byR. Tummala and E. Rymaszewski, and is published by Van NostrandReinhold, 115 Fifth Avenue, New York, N.Y.

A problem with conventional plastic packages is that their internalleadframes limit reduction of the size of the packages. Practitionershave attempted to reduce the size of packages by eliminating internalleadframes, as is shown in U.S. Pat. No. 4,530,152 to Roche et al andU.S. Pat. No. 5,172,214 to Castro, but these packages have numerousdisadvantages. The contacts of the package shown by Roche in the '152patent have orthogonal side surfaces. Accordingly, the packages arebelieved to be unreliable because the contacts could easily be pulledfrom the encapsulant material. The package shown by Castro in the '214patent has leads which extend into the body of the package from a lowerexternal surface of the package to the top of the die. These leads arelarge, and have complex bends. Including such leads in a package wouldincrease manufacturing costs and limit reductions in the lateral size ofthe package. By contrast, the contacts of the packages within thepresent invention are simpler, do not have such bends, and allow forpackages of smaller lateral size.

SUMMARY OF THE INVENTION

The present invention is to directed toward improved plastic packagesfor housing an integrated circuit die, and to leadframes and methods formaking such packages. The packages of the present invention are easierand less expensive to make than conventional plastic packages, and aremore reliable and efficiently-sized than conventional packages.

In one embodiment of an assembly method for a package within the presentinvention, Step 1 provides a metal leadframe. The leadframe includes arectangular frame, e.g., a square frame. A substantially planar die padis within and connected to the frame. A plurality of finger-likerectangular tabs extend from the frame toward the die pad withoutcontacting the die pad. The number and location of the tabs around theframe may vary. The die pad and the tabs have peripheral side surfaceswhich include a reentrant portion(s) and asperities. The reentrantposition(s) and asperities enhance the connection of the die pad andtabs to the plastic encapsulating material.

Step 2 places and attaches an integrated circuit to a first surface ofthe die pad.

Step 3 electrically connects a bond wire or an equivalent conductorbetween each bonding pad of the die and a first surface of one of thetabs.

Step 4 places the leadframe on a flat surface, with the die facingupwards, and applies a viscous encapsulant material onto the upwardfacing first surface of the leadframe. The encapsulant material is thenhardened. The encapsulant material covers the die, the bond wires, afirst surface of the tabs, the first surface of the die pad, the sidesurfaces of the die pad and tabs, and all or part of the frames aroundthe die pad. A lower second surface of the leadframe, including a lowersecond surface of the die pad and tabs, is not covered with encapsulant.

Step 5 plates the exposed surfaces of the leadframe, including theexposed second surfaces of the die pad and tabs with a metal, such ascopper, gold, lead-tin solder, tin, nickel, palladium, or any solderablemetal.

Step 6 cuts the encapsulated portions of the leadframe with a saw. Inparticular, step 6 either obliterates the disposable portions of theleadframe, or severs the disposable portions of the leadframe from othercomponents of the leadframe, such as the die pad and tabs, which are tobe included in the package. Step 6 also trims the encapsulant materialand thereby forms the peripheral sides of the package.

A feature the packages built by the above described method is that thedie pad and contacts (i.e., the severed tabs of the leadframe) of thepackage are located at the lower first surface of the package. The firstsurfaces and side surfaces of the die pad and tabs are internal to thepackage, i.e., covered with encapsulant material, but the secondsurfaces of the die pad and tabs are not covered by encapsulantmaterial. The die pad and tabs are isolated from each other byencapsulant material.

In a completed package, only the encapsulant material holds the die padand contacts to the package. The connection of the encapsulant materialto the die pad and contacts is enhanced by the reentrant portion(s) andasperities of the side surfaces of the die pad and contacts. Thereentrant portions and asperities of the side surfaces of the die padand contacts function as encapsulant fasteners or lead locks.

Numerous variations of the leadframe, package, and assembly methoddescribed above also are described in this application. In onealternative assembly method, a leadframe is provided which allows aplurality of packages to be constructed simultaneously.

A leadframe for constructing a plurality of packages simultaneouslyincludes, for example, a matrix of interconnected rectangular frames. Adie pad is within and connected to each of the interconnected frames. Aset of tabs extend from each frame toward the sides of the enclosed diepad without contacting the die pad. A subsequent encapsulation stepincludes applying an encapsulant material onto the surface of theleadframe to which the dies are attached. This step covers the dies andthe side surfaces of the die pads and tabs within a single block ofencapsulant material. The encapsulant material is then hardened. Acutting step separates individual packages from each other and from thedisposable portions of the leadframe. The cutting step also severs theconnection between each of the interconnected frames and the die pad andtabs within each frame.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a flow chart of a method of making a package.

FIG. 2 is a top view of leadframe used for making a package.

FIG. 3 is an enlarged cross-sectional side view of a circled portion ofFIG. 2. FIG. 3 shows an embodiment of a side surface of a die pad andtab.

FIG. 4 is a first alternative embodiment of a side surface of a die padand tab.

FIG. 5 is a second alternative embodiment of a side surface of a die padand tab.

FIG. 6 is a third alternative embodiment of a side surface of a die padand tab.

FIG. 7 is a top view of the leadframe of FIG. 1 after encapsulation. Thedashed lines are cutting paths for a subsequent sawing step.

FIG. 8 is a cross-sectional side view of a completed package.

FIG. 9 is a cross-sectional side view of the package of FIG. 8 furtherincluding solder interconnection bumps on the package contacts.

FIG. 10 is a flow chart of a method for making a plurality of packagessimultaneously.

FIG. 11 is a top view of a leadframe used for making a plurality ofpackages simultaneously.

DETAILED DESCRIPTION

FIG. 1 shows an exemplary method of assembling a package in accordancewith the present invention. FIG. 8 shows a completed package.

Step 1 of FIG. 1 provides a metal leadframe. FIG. 2 is a top view of afirst embodiment of a metal leadframe 20 in accordance with the presentinvention. For ease of view, shading is used in FIG. 2 to distinguishthe metal portions of leadframe 20 from empty spaces between the variouselements of leadframe 20.

Leadframe 20 of FIG. 2 is planar or substantially planar and is made ofa conventional leadframe metal, such as copper or copper alloys, platedcopper or plated copper alloys, Alloy 42 (42% nickel, 58% iron), orcopper plated steel, depending on the application. The opposing upperand lower surfaces of leadframe 20 may be plated with different metals.For example, the tabs 30 and/or other portions of leadframe 20 whichultimately are enclosed within the package may be plated with silver,gold, nickel palladium, or copper. Such plating, for example, mayenhance attachment of bond wires to tabs 30.

FIG. 2 includes dash lines A—A, B—B, C—C, and D—D. These are lines whichindicate where leadframe 20 is cut in Step 6 of FIG. 1. Step 6 isdescribed below. FIG. 2 also includes a circle and dashed line 3—3,which indicate the view of FIG. 3.

Leadframe 20 of FIG. 2 includes a peripheral rectangular frame 21. Frame21 consists of four rectilinear members. The two intersecting pairs ofparallel members of frame 21 are denoted as members 22 and 22A and 23and 23A. Artisans should understand that the terms “rectangular” or“rectangle” as used herein include a square, which is a rectangle withfour equivalent sides.

A rectangular die pad 24 is within and connected to frame 21. Die pad 24has a planar or substantially planar upper first surface 25 and,although it is not shown in FIG. 2, an opposite planar or substantiallyplanar lower second surface 26. Die pad 24 also has peripheral sidesurfaces 27 between upper first surface 26 and lower second surface 26.

A connector 28 connects two parallel side surfaces 27 of die pad 24 tomembers 22 and 22A of frame 21 of FIG. 2. Each connector 28 includes amushroom-shaped anchor 29, although other shapes may be used for anchor29.

Three finger-like rectangular tabs 30 are connected to and extend frommembers 23 and 23A toward an adjacent side surface 27 of die pad 24without contacting side surfaces 27. As a result of this configuration,the completed package will have a single row of three contacts on twoparallel sides of the package. Tabs 30 ultimately are severed frommembers 23 and 23A along cut lines C—C and D—D of FIG. 2, and become thecontacts of the package.

The number, location, and shape of tabs 30 may vary. For example,instead of having tabs 30 only on members 23 and 23A of frame 21 ofleadframe 20, as in FIG. 2, sets of tabs 30 may be placed on all fourmembers of frame 21. This alternative embodiment would result in theformation of a quad package.

Each tab 30 of FIG. 2 has a planar or substantially planar upper firstsurface 31 and, although it is not shown in FIG. 2, an opposite planaror substantially planar lower second surface 32. Each tab 30 also hasthree peripheral side surfaces 33 between upper first surface 31 andlower second surface 32.

FIGS. 3–6 show an enlarged cross-sectional side view of the circledportion of FIG. 2 along line 3—3. In particular, FIGS. 3–6 show, inaccordance with the present invention, a side surface 27 of a die pad 24and a side surface 33 of a tab 30 of leadframe 20 of FIG. 2.

Side surface 27 of die pad 24 and side surface 33 of tab 30 of FIG. 3have reentrant portions. In particular, the upper and lower portions ofside surfaces 27 and 33 are reentrant such that there is a central peak34 which extends outward from side surfaces 27 and 33 of die pad 24 andtab 30, respectively. Encapsulant material flows into the reentrantportions of side surfaces 27 and 33. Central peak 34 extends into theencapsulant material.

The reentrant portions of side surfaces 27 of die pad 24 and sidesurfaces 33 of tabs 30 of FIG. 3 have the function, in a completedpackage, of enhancing the connection between the encapsulating material,on the one hand, and die pad 24 and the contacts of the package (i.e.,severed tabs 30), on the other hand.

In addition to having reentrant portions, side surface 27 of die pad 24and side surface 33 of tab 30 of FIG. 3 have a roughly-textured surfacewhich includes numerous asperities. Encapsulant material flows into theareas of the asperities. The asperities also enhance the connectionbetween the encapsulant material and die Dad 24 and the contacts of thepackage (i.e., the severed tabs 30).

FIG. 4 shows a first alternative profile for side surfaces 27 of die pad24 and side surfaces 33 of tabs 30 of leadframe 20 of FIG. 2. In theembodiment of FIG. 4, side surfaces 27 and 33 each have a centraldepression 35 and a roughly-textured surface which includes numerousasperities. Encapsulant material flows into central depression 35 and inthe areas of the asperities. The reentrant portion and asperities ofside surfaces 27 and 33 of FIG. 4 have the function, in a completedpackage, of enhancing the connection between the encapsulant materialand die pad 24 and the contacts of the package (i.e., the severed tabs30).

FIG. 5 shows a second alternative profile for side surfaces 27 of diepad 24 and side surfaces 33 of tabs 30 of leadframe 20 of FIG. 2. In theembodiment of FIG. 5, side surfaces 27 and 33 include a rounded lip 36adjacent to upper surface 25 and 31 of die pad 24 and tab 30,respectively. Lip 30 has a roughly-textured surface which includesnumerous asperities. Side surfaces 27 and 33 also have a reentrantorthogonal portion 37 beneath lip 36, adjacent to lower second surface29 and 32 of die pad 24 and tab 30, respectively. Encapsulant materialflows beneath lip 36 and into the area of the asperities. Like theembodiments of FIGS. 3 and 4, the reentrant portions and asperities ofside surface 27 of die pad 24 and side surface 33 of tab 30 of FIG. 5have the function, in a completed package, of enhancing the connectionbetween the encapsulant material and die pad 24 and the contacts of thepackage (i.e., tabs 30 after they are severed from members 23 and 23A).

FIG. 6 shows a third alternative for side surfaces 27 of die pad 24 andside surfaces 33 of tabs 30 of leadframe 20 of FIG. 1. In thisembodiment, side surfaces 27 and 33 each include a rectangular lip 38adjacent to upper surface 25 and 31 of die pad 24 and tab 30,respectively. Side surfaces 27 and 33 also have a reentrant orthogonalportion 39 beneath lip 38 adjacent to lower second surface 29 and 32 ofdie pad 24 and tab 30, respectively. Encapsulant material flows beneathlip 38. Like the embodiments of FIGS. 3–5, the reentrant portions ofside surface 27 of die pad 24 and side surface 33 of tab 30 of FIG. 6have the function, in a completed package, of enhancing the connectionbetween the encapsulant material and die pad 24 and the contacts of thepackage (i.e., severed tabs 30).

As discussed above, Step 1 of FIG. 1 provides a metal leadframe havingfeatures like those shown in FIG. 2 and either FIG. 3, 4, 5, or 6, orequivalents thereof. Leadframe 20 of FIG. 2 is formed from rolled stripmetal stock by wet chemical etching or mechanical stamping usingprogressive dies.

As is well known, chemical etching (also known as chemical milling) is aprocess that uses photolithography and metal-dissolving chemicals toetch a pattern into a metal strip. The photoresist is exposed toultraviolet light through a photo mask having a desired pattern, and issubsequently developed and cured. Chemicals are sprayed or otherwiseapplied to the masked strip, and exposed portions of the strip areetched away, leaving the desired pattern.

As is also well known, progressive stamping uses sets of progressivedies to mechanically remove metal from a metal strip. Each of aplurality of stamping stations uses one of the dies to punch a distinctsmall area of metal from the strip as the strip moves through thestations.

A leadframe 20 having side surfaces like FIG. 3 can be formed bychemically etching the rolled strip metal stock from both sides using aconventional liquid etchant. The etch process is stopped early so thatthere is an underetching of all of the side surfaces of the componentsof leadframe 20, including side surfaces 27 of die pad 24 and sidesurfaces 33 of tabs 30, compared to the time it would take to formvertical side surfaces. The size and shape of central peak 34 of FIG. 2is controlled by the amount of underetching.

A leadframe 20 having side surfaces like FIG. 4 can be formed bychemically etching the rolled strip metal stock from one side using aconventional liquid etchant. The etch process is continued beyond thetime required to form orthogonal side surfaces for the components ofleadframe 20. The size and shape of central depression 35 of FIG. 3 iscontrolled by the amount of overetching.

A leadframe 20 having side surfaces like FIG. 5 can be formed in a twostep process. The first step of such a process involves forming aleadframe 20 by chemical etching or progressive stamping so that theside surfaces of the components of leadframe 20, including die pad 24and tabs 30, have an orthogonal profile. The second step involvescoining the upper first surface of the leadframe 20, that is, applying ahigh pressure impact to the upper first surface of the leadframe 20.This step deforms the side surfaces of leadframe 40 adjacent to theimpacted surface so that the rounded, asperity-marked protruding lip 36of FIG. 5 is formed.

A leadframe 20 having side surfaces like FIG. 6 can be formed byprogressive stamping. The side surfaces of the components of leadframe20, including side surfaces 27 of die pad 24 and the side surfaces 33 oftabs 30, can be provided with a rectangular lip 38 and a reentrantorthogonal portion 39 by including intermediate stamping steps which donot fully cut through the rolled strip metal stock before finallycutting through the rolled strip sheet. The intermediate stamping stepsand the final cutting steps combine to form the rectangular, protrudinglips 38 of side surfaces 27 and 33 of FIG. 5.

Step 2 of FIG. 1 places an integrated circuit die onto upper firstsurface 25 of die pad 24. The placement and attachment of the die ontodie pad 24 may be performed using a conventional die attach machine andconventional die attach adhesives. During Step 2 and the subsequentassembly steps, leadframe 20 of FIG. 2 is grounded to protect againstelectrostatic discharge (“ESD”).

Step 3 of FIG. 1 electrically connects a conductive metal bond wirebetween individual bonding pads on the integrated circuit die and theupper first surface 31 of individual tabs 30 on leadframe 20 of FIG. 2.Tabs 30 ultimately become contacts in the completed package, after tabs30 are severed from members 23 and 23A of frame 21. Conventional bondwire attachment equipment may be used for Step 3. Leadframe 20 of FIG. 2is grounded during this wiring step to prevent damage to the integratedcircuit dies due to electrostatic discharge. At the completion of Step3, each bonding pad of each die is electrically connected to a tab 30 ofleadframe 20 of FIG. 1, which is grounded. Tabs 30 of leadframe 20 areall shorted together, which facilitates ESD protection.

In Step 4 of FIG. 1, the lower second surface of leadframe 20 of FIG. 2is placed on a flat surface, and a viscous adhesive encapsulatingmaterial is applied onto the upward facing upper first surface ofleadframe 20. The encapsulating material is applied so that theencapsulating material covers: the integrated circuit die; the bondwires; any exposed peripheral portions of upper first surface 25 of diepad 24 around the die; side surfaces 27 of die pad 24; upper firstsurface 31 of tabs 30; side surfaces 33 of tabs 33; and part or all ofthe width of members 22, 22A, 23, and 23A of frame 21. The encapsulantmaterial also fills the empty spaces between the components within frame21 of leadframe 20. The encapsulant material does not, however, coverlower second surface 26 of die pad 24 or lower second surfaces 32 oftabs 30 of FIG. 2. In an alternative embodiment, die pad 24 may be upset during the encapsulation step so that a thin layer of encapsulantmaterial forms under lower second surface 26 of die pad 24. If such astep were used, die pad 24 would be completely internal to the package.Finally, the encapsulant material is hardened.

There are several methods by which Step 4 of FIG. 1 may be accomplished,depending on the application. For example, as a first step, leadframe 20of FIG. 2 is placed on a horizontal surface. As a second step, acontiguous bead of a conventional hardenable viscous adhesive material,such as HYSOL 4451 epoxy from the Dexter-Hysol Company of City ofIndustry, California, is applied onto the upper first surface of sidemembers 22, 22A, 23, and 23A of frame 21 of leadframe 20 of FIG. 2,forming a closed rectangular dam. As a third step, the dam issolidified, such as by heating at 150° C. for one hour. As a fourthstep, a conventional hardenable viscous adhesive material suitable forencapsulating packages, such as HYSOL 4450 encapsulant, is appliedwithin the dam so that the incomplete package within the dam is coveredwith encapsulant material. As a final step, the encapsulant material ishardened, such as by heating at 150° C. for one hour, forming a singlesolid block of encapsulant material above and on leadframe 20, includingon its side surfaces.

Alternatively, Step 4 of FIG. 1 may be accomplished using conventionalplastic molding techniques. In such a method, leadframe 20 of FIG. 2 isplaced in a mold, and a single block of solid molded encapsulantmaterial is formed above and on leadframe 20, including on its sidesurfaces. The encapsulant material may be a conventional plastic moldingcompound applied using conventional techniques. Example moldingcompounds include NITTO MP-8000AN molding compound from the NittoCompany of Japan, and EME 7351 UT molding compound from the SumitomoCompany of Japan. Conventional gates may be formed in leadframe 20 toassist in the molding process.

In Step 5 of FIG. 1, the portions of leadframe 20 of FIG. 2 which arenot covered with the encapsulant material, including lower secondsurface 26 of die pad 24 and lower second surfaces 32 of tabs 30, areplated using a conventional plating metal compatible with printedcircuit boards. For example, exposed second surfaces 26 and 33 of diepad 24 and tabs 30, respectively, may be plated with gold, nickelpalladium, inconel, lead tin solder, or tantalum, depending on theapplication. The plating step is facilitated by the electricalinterconnection of the components of leadframe 20.

FIG. 7 is a top view of leadframe 20 of FIG. 2 after the completion ofSteps 1–5 of FIG. 1. A rectangular block of hardened encapsulantmaterial 40 covers the upper first surface of leadframe 20. Although notshown, encapsulant material 40 also covers side surfaces 27 and 33 ofdie pad 24 and tabs 30, respectively, of leadframe 20. The block ofencapsulant material 40 in FIG. 7 covers a portion of the width ofmembers 22, 22A, 23, and 23A of frame 21 of leadframe 20. The peripheralportions of members 22, 22A, 23, and 23A of frame 21 remain exposed.Alternatively, encapsulant material 40 could be deposited over theentire upper first surface of leadframe 20. As a second alternative,encapsulant material 40 could be deposited within frame 21 so that tabs30 are covered, but members 22, 22A, 23, and 23A are not covered.

Step 6 of FIG. 1 cuts leadframe 20 of FIG. 7 in situ. Referring to FIGS.2 and 7, Step 6 severs the connection between tabs 30 and members 23 and23A of frame 21 of leadframe 20. Step 2 also severs connectors 28between die pad 24 and members 22 and 22A of frame 21 of leadframe 20.Step 6 also cuts encapsulant material 40, forming vertical external sidesurfaces of the package. Finally, Step 6 completes the formation of thepackage by cutting a completed package away from the disposable portionsof leadframe 20.

Step 6 may be performed using a saw or other shearing apparatus. Toperform Step 6 using a saw, the encapsulated leadframe 20 of FIG. 7 isinverted and placed on sticky film. Using the exposed portions ofleadframe 20 as a guide (see FIG. 2), a conventional wafer saw is usedto saw a completed package from the encapsulated leadframe 20.Criss-crossing rectilinear cuts are made along dashed lines A—A, B—B,C—C, and D—D of FIGS. 2 and 7 so that the disposable portions ofleadframe 20, including side members 22, 22A, 23, and 23A of frame 21,connectors 28 and anchors 29, are cut away from the package, isolatedwithin encapsulant material 40, or obliterated by the saw. The cuttingpath of the saw and/or the width of the saw blade should be selected sothat the connections between tabs 30 and members 23 and 23A are severedand side members 22, 22A, 23, and 23A are cut away or obliterated, butall or most of each tab 30 remains intact.

FIG. 8 is a cross-sectional side view of an exemplary package 50 madefrom leadframe 20 of FIG. 2 according to Steps 1–6 of FIG. 1. Package 50has a planar or substantially planar external upper first surface 51,and an opposite planar or substantially planar external lower secondsurface 52. Orthogonal external package sides 57 are at the periphery ofpackage 50 between upper first surface 51 and lower second surface 52.Sides 57 were formed during Step 6, when encapsulant material 40 andtabs 30 were cut.

Lower second surface 52 of package 50 of FIG. 8 consists of die pad 24,a plurality of peripheral contacts 53, and hardened encapsulant material40. Die pad 24 and each contact 53 are like islands at the lowerexternal second surface 52 of package 50. They are physically separatedfrom each other by encapsulant material 40.

Die pad 24 and contacts 53 of FIG. 8 are vestiges of leadframe 20 ofFIG. 2. Referring to FIGS. 2 and 8, contacts 53 of package 50 of FIG. 8were formed when the connections between tabs 30 and members 23 and 23Awere severed by the saw during Step 6.

Die pad 24 of FIG. 8 is rectangular and is located at lower secondsurface 52 of package 50. Die pad 24 includes a planar or substantiallyplanar upper first surface 25, an opposite planar or substantiallyplanar second surface 26, and peripheral side surfaces 27. Secondsurface 26 of die pad 24 is in the same plane as lower second surface 52of package 50 in FIG. 8, although in alternative embodiments, die pad 24may be set up into encapsulant material 40.

Although not fully shown in FIG. 8, rectangular die pad 24 has four sidesurfaces 27 (only two are shown). Each side surface 27 of die pad 24 hasa reentrant portion(s), as exemplified by FIGS. 3–6. In addition, sidesurface 27 may have asperities, as exemplified by FIGS. 3–5.

In FIG. 8, integrated circuit die 56 is on and attached to upper firstsurface 25 of die pad 24. Peripheral portions of upper first surface 25are covered by encapsulant material 40. Side surfaces 27 of die pad 24also are covered by encapsulant material 40. Lower second surface 26 ofdie pad 24 is not covered encapsulant material 40, but rather is exposedat lower external surface 52 of package 50. In an alternative embodiment(not shown), die pad 24 may be entirely internal to encapsulant material40 of package 50.

Two contacts 53 are shown in package 50 of FIG. 8, but since package 50was constructed from leadframe 20 of FIG. 2, it should be understoodthat package 50 has a set of three contacts 53 on two sides 57 ofpackage 50. In alternative embodiments, package 50 could be formed witha different number or arrangement of contacts, depending on theapplication.

Each contact 53 of FIG. 8 has a substantially rectangular perimeter andis located at the lower second surface 52 of package 50. Each contact 53includes a planar or substantially planar upper first surface 31, anopposite planar or substantially planar second surface 32, threeinternal side surfaces 33 (only one is shown in FIG. 8) having reentrantportions, and one external orthogonal side surface 55. Second surface 32of contact 53 is in the same plane as lower second surface 52 of package50.

First surface 31 and side surfaces 33 of contacts 53 are covered with anencapsulant material. Second surface 32 and external side surface 55 ofcontacts 53 are not covered with encapsulant material.

Orthogonal external side surfaces 55 of contacts 53 of FIG. 8 wereformed during Step 6 of FIG. 1 when the saw cut the connections betweentabs 30 and members 23 and 23A of leadframe 20 of FIG. 2. Accordingly,the external side surface 55 of each contact 53 has a vertical profilewhich is the same plane as the corresponding vertical side 57 of package50.

Although not shown in FIG. 8, the three internal side surfaces 33 onlyone is shown) of each contact 53 have reentrant portions, as exemplifiedby FIGS. 3–6. In addition side surfaces 33 may have asperities, asexemplified by FIGS. 3–5. Both the reentrant portion(s) and asperitiesof contacts 53 enhance the connection between contacts 53 andencapsulant material 40 of package 50 of FIG. 8.

The perimeter of contacts 53 need not be substantially rectangular inshape. For example, if tabs 30 of leadframe 20 of FIG. 2 had a circularperimeter, then contacts 53 would have a largely circular perimeter witha rectilinear portion formed during the cutting of tab 30 from leadframe20 in Step 6.

A bond wire 58 is connected between each bonding pad 56 a of die 56 andthe upper first surface 31 of each contact 53. Bond wire 58 electricallyconnects individual bonding pads 56 a of die 56 to individual contacts53.

Second surface 32 of contacts 53 of FIG. 8 may be directly connected toan external printed circuit board, as in an LCC package. Alternatively,a solder interconnection bump may be formed on contacts 53 forphysically and electrically connecting package 50 to a printed circuitboard. FIG. 9 shows a solder interconnection bump 60 formed on lowersecond surface 32 and external side surface 55 of each contact 53 ofpackage 50 of FIG. 8.

In an alternative embodiment, second surface 26 of die pad 24 also maybe connected, such as by solder paste, to the printed circuit board tofacilitate package cooling. The cooling occurs by thermal conduction.

FIG. 10 is a flow chart for an alternative assembly method, inaccordance with the present invention, for constructing a package likethat of FIG. 8. In the method of FIG. 10, a plurality of packages areconstructed simultaneously. The basic steps of the FIG. 10 process arethe same as the FIG. 1 process.

Step 1 of FIG. 10 provides a thin metal leadframe which includes aplurality of interconnected rectangular frames in a matrix. A die pad isprovided within each frame.

FIG. 11 shows an exemplary metal leadframe 70, in accordance with thepresent invention, suitable for Step 1 of FIG. 10. Shading is used inFIG. 11 to distinguish metal portions of leadframe 70 from empty spacebetween the components of leadframe 70.

Leadframe 70 of FIG. 11 is planar or substantially planar and is formedof metal. The metals and methods used for constructing leadframe 70 arethe same as those described above for leadframe 20 of FIG. 2.

Leadframe 70 of FIG. 11 includes a disposable rectangular outer frame71. Outer frame 71 consists of four intersecting members, denoted asmembers 72–75. Member 72 is parallel to member 74, and member 73 isparallel to member 75.

Within outer frame 71 of FIG. 11 are four interconnected rectangularframes in a two by two matrix. These frames are formed by theintersection of three disposable strips 76 and three disposable strips77. Each of the four interconnected frames of FIG. 11 has the same basicfeatures as frame 21 of FIG. 2. Accordingly, the same reference numberswill be used, where applicable, and associated discussion will beabbreviated.

A rectangular die pad 24 is within and connected to each of the fourframes formed by strips 76 and 77 of FIG. 11. As in FIG. 2, each die pad24 of FIG. 11 has four side surfaces 27. Each side surface 27 has areentrant portion(s), such as in the examples of FIGS. 3–6. Sidesurfaces 27 also may include asperities, such as those shown in FIGS.3–5.

Three parallel strips 76 are within and connected to frame 71 of FIG.11. A first strip 76 is adjacent to, parallel to, and connected tomember 72 of frame 71. A second strip 76 is adjacent to, parallel to,and connected to member 74 of frame 71. A third strip 76 is located inthe center of frame 71 between juxtaposed pairs of die pads 24. Eachstrip 76 of FIG. 11 is connected to each of the die pads 24 which areadjacent to that particular strip 76. A disposable mushroom-shapedanchor 29 connects each strip 76 to each adjacent die pad 24. Twodisposable connectors 78 connect member 72 to its adjacent strip 76, andtwo connectors 78 connect member 74 to its adjacent strip 76. The numberand locations of connectors 76 may vary.

Three parallel strips 77 also are within and connected to frame 71 ofFIG. 11. One strip 77 is adjacent to, parallel to, and connected to sidemembers 73 and 75 of frame 71. A disposable connector 78 connectsmembers 73 and 75 to their respective adjacent strip 77. A third strip77 is located in the center of frame 71 between juxtaposed pairs of diepads 24.

The intersecting ends of the peripheral strips 76 and 77 of FIG. 11 areconnected to the inner corners of outer frame 71. A gate 79 extends atapproximately a 45 degree angle from each of the four inner corners offrame 71 and connects to the interconnected ends of peripheral strips 76and 77. Gate 79 is useful for the introduction of molding compound intoa mold, where molding is the chosen method of encapsulation.

Central strip 76 of FIG. 11 intersects central strip 77 at the center ofleadframe 70. The ends of central strips 76 and 77 intersect theperipheral strips 77 and 76, respectively.

In FIG. 11, a plurality of straight, evenly-spaced, finger-like,rectangular tabs 30 extend in sets of five from each strip 77 toward thesides of each of the die pads 24 adjacent that particular strip 77. Tabs30 do not contact die pads 24. The central strip 77 that is betweenjuxtaposed pairs of die pads 24 has mirror-image sets of five tabs 30which extend in opposite directions toward each of the juxtaposed diepads 24. Each tab 30 will ultimately form a contact 53 of package 50 ofFIG. 8.

Each tab 30 of FIG. 11 has three side surfaces 33 which have a reentrantportion(s), such as shown in FIGS. 3–6. Side surfaces 33 of tabs 53 alsomay include asperities, such as those shown in FIGS. 3–5. The reentrantportions and asperities of side surfaces 33 of tabs 30 enhance theconnection between encapsulant material 40 and contacts 53 (i.e.,severed tabs 30) of a completed package 10 of FIG. 8.

Step 2 of FIG. 10 places and attaches an integrated circuit die 56 onupper first surface 25 of each die pad 24 of leadframe 70 of FIG. 11, asdescribed above for Step 2 of FIG. 1.

Referring to FIGS. 8 and 11, Step 3 of FIG. 10 electrically connects aconductive metal bond wire 58 between each bonding pad 56 a on eachintegrated circuit die 56 attached to leadframe 70 and a tab 30. Bondwire 58 is connected to the first surface 31 of each tab 30. The methodsfor Step 3 of FIG. 11 are the same as described above for Step 3 of FIG.1.

Step 4 of FIG. 10 covers each incomplete package of leadframe 70 of FIG.11, including all of the dies 56, with a conventional viscous, adhesiveencapsulant material. The methods and materials used for Step 4 of FIG.10 are the same as for Step 4 of FIG. 1, except that the encapsulantmaterial is applied onto all of the incomplete packages 50 of leadframe70 of FIG. 11. The encapsulant material covers the upper first surfaceof leadframe 70, as well as side surfaces 27 and 33 of die pads 24 andtabs 33, respectively. The encapsulant material is then hardened into asingle block which covers all of the incomplete packages of leadframe 70of FIG. 11, as well as all or part of the width of members 72–75 offrame 71 of leadframe 70. Again, the lower second surface of leadframe70, including lower surfaces 26 and 32 of die pads 24 and tabs 30,respectively, is not covered by encapsulant material, but insteadremains exposed.

Step 5 of FIG. 10 plates the exposed lower surface of leadframe 70 ofFIG. 11, including lower second surfaces 26 and 32 of die pads 24 andtabs 30, respectively, with; a conventional plating metal. This step isaccomplished as described above for Step 5 of FIG. 1.

Step 6 of FIG. 10 cuts leadframe 70 of FIG. 11 after the encapsulationstep. Encapsulated leadframe 70 is cut in situ, similar to leadframe 20of FIG. 7. The disposable portions of leadframe 70 are either severedfrom the packages, obliterated, or isolated by encapsulant material fromthe other components of package 50 of FIG. 8. The requirements of andmethods used for Step 6 of FIG. 10 are basically the same as describedabove for Step 6 of FIG. 1, except that more cuts have to be madebecause leadframe 70 of FIG. 11 is bigger and has more components thanleadframe 20 of FIG. 2.

Step 6 of FIG. 10 severs the connection between tabs 30 and strips 77 ofleadframe 70. This cut forms the isolated, individual contacts 53 shownin package 50 of FIG. 8. Step 6 also severs the connection betweenanchors 29 and strips 76. This cut physically isolates die pads 24within the encapsulant material. Step 6 also cuts through the singleblock of encapsulant material formed during Step 4 to form four packages50 from leadframe 70 of FIG. 11.

Step 6 may be performed using a saw or other cutting apparatus. Where asaw is used for Step 6, the saw is moved along strips 76 and 77 (SeeFIG. 11). The saw blade used should be wider than strips 76 and 77 ofFIG. 11, but narrower than the combined width of central strip 77 andthe back-to-back tabs 30. As a result, moving the saw blade along strips76 and 77 will obliterate strips 76 and 77, but will not obliterate tabs30. As discussed above, the surface area of tabs 30 must be maintainedbecause the severed tabs 30 become contacts 53 in package 50 of FIG. 8.

An exemplary method of accomplishing Step 6 of FIG. 10 includes a firststep of inverting the encapsulated leadframe 70 and placing it on stickypaper. Using the exposed portions of leadframe 70 of FIG. 11 as apattern, three parallel cuts are made, each of which goes through sidemembers 73 and 75 and along and through the length of a strip 76 ofleadframe 70. These three cuts form two of the four external sidesurfaces 57 of package 50 of FIG. 8; obliterate strips 76; and sever theconnections between die pads 24 and strips 76.

Next, the encapsulated leadframe 70 is rotated 90 degrees, and threeparallel cuts are made perpendicular to the original three cuts. Each ofthese latter three cuts goes through side members 72 and 74 and alongand through the length of a strip 77. These latter three cuts also formthe remaining two external side surfaces 57 of package 50 of FIG. 8.Since the width of the saw blade is selected to be wider than strips 76and 77, but narrower than the combination of central strip 77 and tabs30, the latter three cuts obliterate strips 77 but do not obliterate thetabs 30 which are attached to strips 77.

The six cuts described above complete the formation of the four packages50 from leadframe 70 of FIG. 11 by separating the completed packagesfrom one another and from the disposable portions of leadframe 70.

Artisans will appreciate that numerous variations of the packages,leadframes, and assembly methods described above are possible. As oneexample, changes can be made to leadframe 70 of FIG. 11 in order tochange the size, shape and numbers of the packages 50 (FIG. 7) formedfrom leadframe 70. For example, instead of simultaneously forming fourpackages using a leadframe like leadframe 70 of FIG. 11, the size of theleadframe may be adjusted so that two, eight, sixteen, forty-eight orsome other number of packages are formed simultaneously. As anotherexample, one may multiply the number of packages formed simultaneouslyby forming several leadframes 70 adjacent to each other on a singlestrip of rolled stock, and processing all of the leadframes 70 on thestrip simultaneously. As another example, the peripheral shapes of diepads 24 and tabs 30 may be changed from rectangular to some other shape.

In addition, the profiles of side surfaces 27 and 33 of die pads 24 andtabs 30, respectively, can be altered from the embodiments of FIGS. 3–6,provided that the function of enhancing the connection betweenencapsulant material 40 and the die pads 24 and contacts 53 of packages50 of FIG. 8 is maintained.

Leadframe 70 of FIG. 11 may be modified in other ways as well. Forexample, the peripheral strips 76 and 77 that are adjacent to members72–75, may be omitted. In such a case, the anchors 29 of FIG. 11 wouldbe attached to members 72 and 74, and tabs 30 would be attached tomembers 73 and 75 of frame 71 of leadframe 70.

As a final example, instead of forming a single block of encapsulantmaterial over all of the dies and incomplete packages of leadframe 70 ofFIG. 11, a mold having individualized cavities for forming a block ofencapsulant material above each the four interconnected frames and diepads 24 of leadframe 70 may be used. In such a case, less encapsulantmaterial would be cut in Step 6 of FIG. 10.

The above description of embodiments of this invention is intended to beillustrative and not limiting. Other embodiments of this invention willbe obvious to those skilled in the art in view of the above disclosure.

1. A package for an integrated circuit die comprising: a die pad havinga first die pad surface, a second die pad surface which is opposite thefirst die pad surface, and a peripheral die pad side surface whichextends between the first and second die pad surfaces; a plurality ofcontacts, each of the contacts having a first end which includes a firstend surface, a second end which is opposite the first end and includes asecond end surface, a first contact surface, a second contact surfacewhich is opposite the first contact surface, and opposing contact sidesurfaces which extend between the first and second ends and the firstand second contact surfaces; an integrated circuit die disposed on thefirst die pad surface; at least one conductor electrically connected toand extending between the die and the first contact surface of arespective one of the contacts; a package body formed of an encapsulantmaterial which covers the die, wherein at least portions of the secondcontact surface and the second end surface of each of the contacts areexposed in the package body; and a bump disposed on at least a portionof the second contact surface of each of the contacts for connecting thepackage to an underlying substrate; the die pad side surface including ameans for vertically locking the die pad to the package body, and atleast the first end surface of each of the contacts including a meansfor vertically locking the contacts to the package body.
 2. The packageof claim 1 wherein the bump is further disposed on at least a portion ofthe second end surface of each of the contacts.
 3. The package of claim1 wherein the second die pad surface of the die pad is at leastpartially exposed in the package body.
 4. The package of claim 1 whereinthe package body defines exterior side surfaces, and at least a portionof the second end surface of each of the contacts is exposed in arespective one of the side surfaces of the package body.
 5. The packageof claim 1 wherein the first die pad surface and the first contactsurface of each of the contacts extend in generally co-planar relationto each other.
 6. The package of claim 1 wherein the means forvertically locking the contacts to the package body is further includedon the contact side surfaces of each of the contacts.
 7. The package ofclaim 1 wherein the second die pad surface is fully covered by thepackage body.
 8. A package for an integrated circuit die comprising: adie pad having a first die pad surface, a second die pad surface whichis opposite the first die pad surface, and a peripheral die pad sidesurface which extends between the first and second die pad surfaces; aplurality of contacts, each of the contacts having a first end whichincludes a first end surface, a second end which is opposite the firstend and includes a second end surface, a first contact surface, a secondcontact surface which is opposite the first contact surface, andopposing contact side surfaces which extend between the first and secondends and the first and second contact surfaces; an integrated circuitdie disposed on the first die pad surface; at least one conductorelectrically connected to and extending between the die and the firstcontact surface of a respective one of the contacts; a package bodyformed of an encapsulant material which covers the die, wherein at leastportions of the second contact surface and the second end surface ofeach of the contacts are exposed in the package body; and means disposedon at least a portion of the second contact surface of each of thecontacts for connecting the package to an underlying substrate; the diepad side surface including a means for vertically locking the die pad tothe package body, and at least the first end surface of each of thecontacts including a means for vertically locking the contacts to thepackage body.
 9. The package of claim 8 wherein the means for connectingthe package to an underlying substrate is further disposed on at least aportion of the second end surface of each of the contacts.
 10. Thepackage of claim 8 wherein the second die pad surface of the die pad isat least partially exposed in the package body.
 11. The package of claim8 wherein the package body defines exterior side surfaces, and thesecond end surface of each of the contacts is at least partially exposedin a respective one of the side surfaces of the package body.
 12. Thepackage of claim 8 wherein the first die pad surface and the firstcontact surface of each of the contacts extend in generally co-planarrelation to each other.
 13. The package of claim 8 wherein the means forvertically locking the contacts to the package body is further includedon the contact side surfaces of each of the contacts.
 14. The package ofclaim 8 wherein the second die pad surface is fully covered by thepackage body.
 15. A package for an integrated circuit die, the packagebeing connected to an underlying substrate and comprising: a die padhaving a first die pad surface, a second die pad surface which isopposite the first die pad surface, and a peripheral die pad sidesurface which extends between the first and second die pad surfaces; aplurality of contacts, each of the contacts having a first end whichincludes a first end surface, a second end which is opposite the firstend and includes a second end surface, a first contact surface, a secondcontact surface which is opposite the first contact surface, andopposing contact side surfaces which extend between the first and secondends and the first and second contact surfaces; an integrated circuitdie disposed on the first die pad surface; means for electricallyconnecting the die to at least one of the contacts; a package bodyformed of an encapsulant material which covers the die, wherein at leastportions of the second contact surface and the second end surface ofeach of the contacts are exposed in the package body; and means disposedon at least portions of the second contact surface and the second endsurface of each of the contacts connecting the package to the underlyingsubstrate; the die pad side surface including a means for verticallylocking the die pad to the package body, and at least the first endsurface of each of the contacts including a means for vertically lockingthe contacts to the package body.
 16. The package of claim 15 whereinthe second die pad surface of the die pad is at least partially exposedin the package body.
 17. The package of claim 15 wherein the packagebody defines exterior side surfaces, and the second end surface of eachof the contacts is at least partially exposed in a respective one of theside surfaces of the package body.
 18. The package of claim 15 whereinthe first die pad surface and the first contact surface of each of thecontacts extend in generally co-planar relation to each other.
 19. Thepackage of claim 15 wherein the means for vertically locking thecontacts to the package body is further included on the contact sidesurfaces of each of the contacts.
 20. The package of claim 15 whereinthe second die pad surface is fully covered by the package body.